1. Field of the Invention
The present invention relates to multicasting and video distribution techniques by content networks configured for providing broadcast-type data via Internet Protocol (IP) based routers.
2. Description of the Related Art
Multicasting enables a broadcast source to broadcast IP-based packets carrying media information (e.g., audio, video, etc.) to multiple destinations such as client computers. In particular, server-based multicasting has required a media server to respond to a client having requested the media stream by initiating a corresponding media stream for the client. Such client-server based multicasting limits the capacity of the multicasting to a limited number of client requests.
IP-based multicasting, however, contemplates that the broadcast source can save bandwidth and central processing unit (CPU) resources by outputting a single broadcast stream to IP-based routers within a network: the IP-based routers copy the broadcast stream on multiple downstream (i.e., ingress) interfaces, enabling wide distribution of the broadcast stream in a scalable manner. Both IPv4 and IPv6 specify multicast addresses in terms of group identifiers, although their use is limited to identification of a reception group.
One limited form of broadcasting within a subnetwork (i.e., subnet) is network-directed broadcast. In particular, host computers in a local area network typically are configured with an IP address, and include a subnet mask that is used to specify the range of IP addresses within a given subnetwork. For example, a host computer having an IP address “123.156.176.234” having a subnet mask of “255.255.255.000” will belong to the subnet “123.156.176”. Hence, all host computers having the IP address prefix “123.156.176” belong to the same subnet.
Consequently, a router can broadcast a packet within its subnetwork using a network-directed broadcast packet. In particular, if a router wants to ping all the host computers on the subnet, if the subnet mask is a 24-bit mask (e.g., 255.255.255.0), the router can ping all the devices automatically by generating a prescribed multicast address based on the subnet prefix (“123.156.176/18”) masked by the subnet mask (“255.255.255.0”), resulting in the multicast address “123.156.176.000”. (Note that the addresses “0” and “255” on a given subnet are reserved for broadcast).
Since the multicast address (e.g., “123.156.176.000”) is a globally valid IP address, any router in the Internet that receives the packet specifying the multicast address (“123.156.176.000”) will be able to route the packet to the destination router serving the subnet “123.156.176/18” (i.e., the destination router). In response to the destination router detecting the packet specifying the multicast address (“123.156.176.000”) within its corresponding destination address field, the destination router will detect the address suffix “000” as corresponding to a network-directed broadcast packet and not a host-specific unicast packet; hence, the destination router will respond to the broadcast address suffix “000” by broadcasting the packet on all its downstream (i.e., ingress) ports, typically using a layer 2 (IEEE 802.1/Ethernet) based multicast address.
As apparent from the foregoing, the network-directed broadcast is limited to broadcast operations in the destination router serving the specified subnet. Hence, any network-directed broadcast capabilities are limited to the members of the subnet. Consequently, broadcast capabilities for a given host computer are limited by the network topology, limiting flexibility in distribution of broadcast information to different destinations.